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中文摘要：
为了解决低轨卫星网络中现有典型源组播算法的信道资源浪费问题,提出了一套单核共享树组播算法,即核心群合并共享树（CCST）和加权CCST（w-CCST）算法.CCST算法包括动态近似中心（DAC）选核方法和核心群合并组播路径构建方法.DAC方法根据组成员在网络中的分布情况自适应选择最优核;在核心群合并方法中,以核节点作为初始核心群,通过核心群和剩余组成员的最短路径方法逐步扩展直至整棵组播树构建完成,从而使得组播树的树代价最小,大大提高了网络的传输带宽利用率和传输效率.在w-CCST算法中,可以通过调整加权因子来适度增大树代价、降低端到端传播时延以满足某些端到端时延要求苛刻的实时组播业务.最后,通过仿真与其它算法进行了性能对比,仿真结果说明CCST组播树的平均树代价比其它组播树显著降低,平均端到端传播时延比其它组播树稍高;w-CCST算法的平均端到端传播时延性能好于CCST算法,树代价性能稍差,说明使用加权因子可以在组播树的树代价和端到端传播时延性能之间作折中.
英文摘要：
To resolve the channel resources waste problem of the typical source-based multicast routing algorithm in low earth orbit （LEO） satellite IP networks, this paper proposes a new core-based shared tree algorithm called the core-cluster combination shared tree （CCST） algorithm and its improved version （i. e. the w-CCST algorithm）. The CCST algorithm consists of the dynamic approximate center （DAC） core selection method and the core-cluster combination multicast route construction method. The DAC method can adaptively select the optimal core node according to group distribution in the network. And the core-cluster combination method takes core node and its nearest group member in hops as initial core-cluster, and expands it to construct entire multicast tree with the lowest tree cost stepwise by a shortest path scheme between newly-generated core-cluster and surplus group members, which can greatly improve transport bandwidth utilization and transport efficiency. In the w-CCST algorithm, a weighted factor is used to make tradeoff between tree cost and end-to-end propagation delay. Therefore, tree cost can be increased a bit and meanwhile end-to-end propagation delay is decreased slightly to meet strict end-to-end delay requirements of some real-time multicast applications by adjusting the weighted factor. Performance of the CCST and w-CCST algorithms is compared with severalother algorithms. And simulation results show that average tree cost of the CCST multicast tree is greatly lower than that of multicast tree of other algorithms, and its average end-to-end propagation delay is a bit higher than that of others, while average end-to-end propagation delay of the w-CCST multicast tree is lower than that of the CCST multicast tree.
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